The present invention relates to an optical projection system for a display, in particular, an optical projection system for a head-up display with improved light efficiency.
There are a number of projection functions, wherein a virtual image is generated and is reflected to a viewer via an optically transparent surface, such as a windshield of a motor vehicle. Such displays are, for example, so-called head-up displays (HUD) or head-mounted displays.
A conventional head-up display is known, for example, from DE 10 2010 002 956 A1. Frequently, imagers (such as a DMD, so-called “dot matrix device”), which emit unpolarized light, are used for the above display types. Due to the geometry of these displays, the image information is often reflected via an optically transparent surface (windshield) at an angle, wherein substantially only one polarization direction is reflected (the so-called Brewster angle). The optically transparent surface is hence not very efficient in terms of its reflective properties. However, it is often not possible to provide the optically transparent surface (windshield) with a reflective coating.
In order to produce a sufficiently bright image for the viewer, the image information must be emitted by the imager with high intensity which, on one hand, increases the costs of the imager and, on the other hand, causes undesirable heat-up in the region of the imager.
It is therefore the object of the present invention to increase the luminous efficiency of displays that generate a virtual image and to project the virtual image to a viewer via an optically transparent surface.